1. Field of the Invention
The present invention relates generally to electrical wiring devices, and particularly to electrical wiring devices with night light capabilities.
2. Technical Background
The breaker panel terminates the AC power service provided by the power utility and distributes AC power to one or more branch electric circuits installed in the structure to form an electrical distribution system. Branch electric circuits often include one or more electrical wiring devices, such as receptacle outlets, that accommodate electrical power plugs. Electrical wiring devices are provided in electrically non-conductive housings that are configured to be installed in outlet boxes. The housing includes electrical line terminals that are electrically insulated from electrical load terminals. The line terminals connect the wiring device to conductive wires from the breaker panel. Feed-through load terminals are connected to downstream wiring that is configured to propagate AC power to one or more downstream electrical loads in the branch circuit. Those of ordinary skill in the pertinent art will understand that the term “load” refers to an appliance, a switch, or some other electrically powered device.
Certain types of faults are known to occur in branch electric circuits and electrical wiring systems. These faults represent serious safety issues that may result in fire, shock or electrocution if not addressed properly. Thus, branch electric circuits typically employ one or more electric circuit protection devices. Protective devices employ a circuit interrupter disposed between the line terminals and the load terminals. The circuit interrupter provides power to the load terminals under normal conditions, but breaks electrical connectivity when the protective device detects a fault condition in the load circuit. There are several types of electric circuit protection devices including ground fault circuit interrupters (GFCIs), ground-fault equipment protectors (GFEPs), arc fault circuit interrupters (AFCIs), transient voltage surge suppressors (TVSSs), or surge protective devices (SPDs). This list includes representative examples and is not meant to be exhaustive. Some devices include both GFCIs and AFCIs. As their names suggest, arc fault circuit interrupters (AFCIs), ground-fault equipment protectors (GFEPs) ground fault circuit interrupters (GFCIs), transient voltage surge suppressors (TVSSs), or surge protective devices (SPD's) perform different functions. Electric circuit protective devices may be disposed within a circuit breaker that provides overcurrent protection, receptacle outlets, plugs, etc. Portable electrical wiring devices, e.g., hair dryers, etc., may also have a protective device disposed therein.
Another safety issue that is of great concern relates to the amount of ambient lighting in a given room or space. In a scenario that most people are familiar with, a person entering a darkened room will usually attempt to locate the wall switch and turn the wall switch to the ON position before entering. There are situations where a light switch is not available, or is not readily available. There are other situations where the person entering the darkened room is disinclined to turn the lights ON as a matter of courtesy.
In one approach that has been considered, a portable lighting device may be inserted into an electrical receptacle located in the room to function as a “night light.” While this arrangement may provide a temporary solution to the potentially unsafe condition described above, it has certain drawbacks associated with it. One drawback relates to the fact that once the night light is inserted into the receptacle, it may remain there—day and night—for an extended period of time and represent a waste of energy. After a while, the resident may notice the problem and unplug the light during daylight hours if the space admits natural light. Unfortunately, the resident may forget to plug the light back into the socket until after night fall and finds himself revisiting the darkened room scenario. In addition, once a small night light is unplugged from the receptacle there is the possibility that it will become lost, misplaced, or damaged from excessive handling.
In another approach that has been considered, a light element may be disposed in a wiring device in combination with another functional element such as a receptacle or a light switch. The wiring device is subsequently installed in a wall box or mounted to a panel. While this approach obviates some of the drawbacks described above, there are other drawbacks that come into play. Conventional permanent lighting elements such as incandescent and neon lights have a relatively short life expectancy of only a few years and, therefore, require periodic servicing and/or replacement. This problem is exacerbated by the fact that the light is typically hard-wired to power contacts disposed in the wiring device. As such, the light element is permanently ON, further limiting the light elements life expectancy of the device.
In yet another approach that has been considered, the aforementioned drawbacks are addressed by providing a light sensor, and the associated circuitry, to control the light element. When the sensor detects the ambient light level falling past a certain point, the control circuit turns the light element ON. One design problem associated with using a light sensor to selectively actuate the light element relates to providing a proper degree of isolation between the light sensor and the light element. Conventional devices solve the problem by separating the light sensor and the light element by as great a distance as possible. Because the light sensor must be disposed a sufficient distance away from the light element, it necessarily requires that the lighting assembly be reduced in size to fit the wiring device form factor. Accordingly, conventional devices of this type often fail to provide an adequate amount of illumination for the intended application and, therefore, do not address the safety concern in a satisfactory manner.
In yet another approach that has been considered, a sensor housing has been employed to mechanically couple an ambient light sensor to a circuit board while positioning the sensor as near as possible to a lens positioned on the cover of the device. The sensor housing also prevents any light emitted by light source (e.g., an LED) from being directed toward the light sensor. (Without the isolation housing, the sensor would sense emissions from the night light and the light sensor circuitry would add the night light to the true ambient light levels and would improperly de-energize lamps). One drawback to this approach relates to the lack of available “real estate” within protective wiring devices that include advanced features (such as fault detection in combination with automatic self-test). In other words, using a bulky housing for isolation takes space (within the device) that could be used more productively.
The isolation problem has also been solved by using electronic isolation techniques. Stated generally, false or improper night life turn OFF can be avoided by periodically interrogating the ambient light detector during periods when the night light is OFF. This approach has allowed designers to position LED elements directly adjacent to the ambient light sensor and uses a larger light pipe to direct ambient light toward the sensor and direct LED light into the ambient space via the larger light pipe. The light pipe is coupled to, again, a rather large lens element disposed on the cover of the wiring device. This approach suffers from the same drawbacks associated with using light isolation structures: the large light pipe requires too much real estate on the protective wiring device's circuit board and the corresponding lens requires too much area on the front cover of the device. A similar drawback occurs when a single-gang device is a multi-functional device (e.g., a dual outlet GFCI with test and reset buttons, trip indicator, night light and light sensor). To be specific, the drawback relates to the fact that—in many cases—a reduction of the size of an element (e.g., night light) corresponds to a reduction in its effectiveness. (E.g., a smaller night light typically means that the light output is reduced).
What is needed is an electrical wiring device that is configured to address the drawbacks and needs described above. A light emitting wiring device is needed that provides a sufficient amount of illumination when the ambient light in a given space falls below a safe level. What is also needed is a bidirectional light pipe that can accommodate a light emitting element and a light sensor element disposed at different locations within the wiring device so that light signals from the light emitting element are directed into the ambient environment while ambient light is provided to the light sensor element.